Telephone system



W. BRANDT Oct. 17, 1933.

TELEPHONE SYSTEM Filed Feb. 2, 1933 INVENTOR W. BRANDT EV ATTORNEY Patented Oct. 17, 19 3 3 TELEPHONE SYSTEM Walter Brandt, Vienna, Austria, assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application February 2, 1933, Serial No. 654,838, and in Austria February 15, 1932 18 Claims. (Cl. 179-17) This invention relates to telephone systems and more particularly to systems including selective party lines.

The object of the invention is to provide a 5 simple, efiicient and economical arrangement for controlling the selective association of any one of a plurality of subscribers stations with a single line, both on incoming and on outgoing calls.

According to this invention, in a system having a group of subscribers stations connected by a single line to a central ofiice, slow-acting relays are provided, one for each station, for disconnecting the other stations upon origination of a call from one of the stations, for disconnecting the other stations on a call incoming to one of the stations, and for disconnec ing an associated group of selective impulse-receiving relays rom the line upon origination of a call at any station or upon answer of anincoming call at any station. The slow-acting r lays are also each operatively responsive to the closure of a groun connection upon the origination of a ply for controlling the selective signaling of any,

desired one of the stations. A further feature of this arrangement is the provision of an operating winding and a normally short-circuited winding on the first of two impulsereceiving relays whereby the first relay is rendered slowin releasing to prevent its release upon the receipt or" the first impulse (that is, upon the opening of the circuit through the operating winding). The arrangement is such that the operation'of the second impulse-receiving relay upon the clos ing of the impulse circuit at the end of the first impulse is effective to open the short circuit through the holding winding of the first impulse-receiving relay and thus enable the release of the first relay upon receipt of the second impulse. is the provision of a ring-up relay responsive to ringing current incoming over the line for operatively extending the line to the impulse receiving relays. The reoperation of the ring-up relay in response to ringing current incoming over the line after the station selecting impulses have all A further feature of this arrangement ciatedapparatus includes the relays 85,36, 87, '88

been received-is effective to complete a ringing circuit to the selected station; and the response of the called station is effective to operate the slow acting relay individual to that station and thereby disconnect the ring-up and impul e-- receiving relays I V The drawing which forms a part of this specification illustrates schematically a portion of a telephone system arranged in accordance with the features of this invention.

'Referring to the drawing; 3 Fig. '1 shows schematically a line 'L' common to live subscribersstations S1, S2, S3, S4 and S5, and relay equipment associated with the stations and line;

Fig. 2' shows schematically a line-switch LS at the central oifice individual to the line L and a final selector FS having access to the line L.

Although the arrangement disclosed in the drawing provides-for five stations, it is or" course understood that the invention is generally applicable to party lines with any number of stations; The telephone station apparatus may be of any standard type and includes impulse sending devices (not shown) and keys designated 1, 2, 3, 41

and 5 for use at their respective stations in; originating telephone calls. The relay equipment associated with the line L atthe end remote from the central'ofiice comprises a ring-up relay 60, impulse-receiving relays 61, 62, 53, 64.- and 65 and cut-off relays 11, 21, 31, ll and 51, one for each of the stations. The stations S1, S2, S3, S4 and S5 are connected to the relay equipment by extension lines designated 10, '20, 30, 10 and 50. The line-switch LS, to which the line L connects at the central office may be of any suitable-type and in the drawing is shown as a rotary step-cystep switch having a driving magnet '74, and three banks ofterminals 71, 72, 73 and corre-' sponding double-ended wipers; associated appae ratus includes the relays 75, 76 and 7'7. The terminals of the banks of switch LS terminate trunksleading to first selectors; the conductors 79 connected to one set of these terminals repre sents one of the trunks, the associated first selector not being shown. The line L also termie nates at the central office in the banks of final selectors, one of which FS is represented schematically by the three banks 81, '82 and 83; assoand 89; The final selector FS is arranged to repeat dial impulses received after'a called line has been seized. The conductors represent the trunk incoming to the selector FS from the banks of preceding selectors having access to this final selector.

To further describe the invention, it will be assumed that the subscriber at station S3 initiates a call by removing the receiver from the switchhook in the usual manner and by also operating the key 3. A circuit is thereby completed from ground through the front contact of key 3, over the lower conductor of extension line 30, winding and inner back contact of cut-off relay 31, conductor 6:), middle contacts of relays 51, 41, 31, 21 and 11 in the order named,

over conductor 102 of line L, through the left inner back contact of relay 76 and thewinding of relay '75 to battery at the back contact of relay 7'7. The cut-01f relay 31 in ividual to station S3 and the relay 75' both operate. Upon restoration of key 3 circuit for holding relays 31 and '75 operated is relay 75, inner left back contact of relay '76, conductor 102 of line L, middle back contacts of relays 11 and 21, inner front contact and winding of relay 31, lower conductor of extension line 30, back contact of key 3, through the telephone instrument of station S3, back over the upper conductor of extension line 30, outer front contact of relay 31, cuter back'contacts of relays 21 and 11, conductor 101 of line L, cuter left back contact of relay 76, to ground at the right front contact of relay 75. With relay 3l'operated, an attempt to initiate a call from any other of the five stations will be ineffective, there being no operating circuit for relays 11, 21, 41 or 51. The operation of relay 31 also prevents operation of the ring-up relay in case the line is selected by some one of the final selectors having access thereto on an incoming call, the connection between the operating winding of relay 60 and conductor 102 being opened at the middle back contact of relay 31. The aforementioned operation of relay initiates the operation of switch LS, to select an idle trunk and first selector, by connecting battery through its inner left front contact, the right back contact of relay 76 and the outer left front contact of relay 75 to the winding of driving magnet '74. Each time the interrupter 78 connects'ground to the other end of the winding of magnet 74, the magnet operates f. thereby advancing the brushes of banks '71, 72

and. 73 one step at a time. When an idle trunk is encountered, relay 76 operates in a circuit from ground connected to the sleeve conductor of the associated first selector, through the sleeve j terminal of this trunk in bank '73, through: both windings of relay '76 in series to battery at the inner left front contact of relay 75. In operating, relay '76 short circuits its own right winding thereby increasing the potential of the sleeve terminal of the selected trunk to preventseizure of the same trunk by any other line-switch having access thereto. The operation of relay 76 also opens the circuit for operating the driving magnet 74 and extends conductors 101 and 102 of line L through the left front contacts of relay '76 and through the brushes and selected terminals of banks 71 and 72 to the line conductors of the first selector (not shown) to which these terminals are permanently connected. Further extension of the line L in response to the dialing of the number ofthe desired station, the testing of the called line, the signaling of the station if found idle, and the establishment of the talking path are completed in well known manner. Relay 31 isheld operated in series with the extentraced frombattery through the back contact of relay '77, winding of sion line 30 and conductors 101 and 102, the source of talking current for the calling station being located in one of the selective switches employed in establishing the connection; relay 76 holds over the sleeve conductor of the first selector to a holding ground until the connection is released the usual manner.

Assume next that the line L has been selected and found idle by the final selector F8 on a call incoming to one of the stations S1, S2, S3, S4 and S5. The final selector FS is arranged to repeat dial impulses over line L for controlling the selection of the particular called station, the line relay 85 being connected, over the incoming line 95 and through the preceding switches (not shown) to the calling line (not shown). Upon seizure of line L, a circuit is closed from battery through the windings of relay 89', through sleeve brush 83 of selector FS, and through the winding of relay 7? of line switch LS to ground. Relay 39 operates, short-- circuiting its left winding to guard the line L from seizure by any other final selector. Relay 7'7 thereupon operates, battery being thereby disconnected from conductor 102 of line L to prevent interference with the incoming call by an attempt to originate an outgoing call at any one of the stations. The operating magnets and other apparatus not involved in the doc tion of this. invention have been omitted in the selector FS. With line relay 85 operated, the release relay 86 is also operated, and a circuit is closed for operating the ring-up relay 60 of line L to prepare the impulse-receiving relays of line L for response to impulses in coming to and repeated by the line relay 835 of selector F53. The circuit for operating relay 60 is traced from the ringing current source 90, through the back contact of relay 87, left winding and back contact of relay 88, front contact of relay 86, wiper and terminal of bank 81, over conductor 102 of line L, through the back contacts of relays 11, 2. 31, 11 and 51 in the order named, conductor 69, through the left back contact of relay 60, condenser 67, and the left winding of relay 60 to ground. Relay 88 does not. operate in this circuit. "The operation of relay 60 in response to the signaling current from selector FS closes a circuit from ground through its right winding and right front contact, conductor 68, outer back contact of relays 51, 41, 31, '21 and 11 in. the order named, conductor 101 of line L, terminal and wiper 82 of selector FS, through the right front contact of relay 85 and inductance 91 to battery. Relay 60 is held operated by the current in this circuit after its inner left contacts open the circuit through. the operating winding. With relay 60 operated, theright winding of relay 61 also energized in a circuit from ground at the left back contact of relay 61, through the right back contact of each of. relays 61, 62, 63 and 64 in the order named, outer left front contact of relay 60, right winding of relay 61 to conductor 68, thence to battery through resistance 91 of 86 is slow to release and remains operated during the receipt of dial impulses.- The first release of relay 85 opens the circuit through the right winding of relay and the right winding of relay 61 and closes a circuitfor operating relay 85 reoperates at the end of the first station impulse, but relay 61 remains operated due to its short-circuited left winding. When relay 85 reoperates, conductor 101 of line L is reconnected to battery through inductance 91, thereby again energizing the right winding, of relay 6i and also energizing the right winding of relay 62; the path for energizing relay 62 is traced from conductor 68, through the inner right back contact of relay 60, right winding of relay 62, inner front contacts of relay 61, to ground at the outer right back contact of relay 60. The 0 eration of relay 62 opens the short circuit around the left winding of relay 61 so that this latter relay may immediately release if a second station impulse is received by relay 85. The release of relay 85 in response to a second impulse opens the circuit through the right windings of relays 61 and 62. Relay 61 releases before relay 85 reoperates, but relay 62 remains operated due to its short-circuited left winding. W hen relay 85 reoperates after the second station impulse, the re-connection of conductor 101 to inductance 91 causes the re-energization of the right windingof relay 62 and the energization of the right winding of relay 63. The operation of relay 63 opens the short circuit around the left winding of relay 62 so that relay 62 may immediately release if a third station impulse is received by relay 85. The release of relay 85 in response to a third impulse opens the circuit through the right windings of relays 62 and 63'. Relay 62 releases before relay 85 reoperates, but relay 63 remains operated due to its shortcircuited left winding. When relay 85 reoperates after the third station impulse, the re-connection of conductor 101 to inductance 91 causes the re-energization ofthe right windingof relay 63 and the energization of the right winding of relay 64. the short circuit around the left winding of relay 63 so that relay 63 may immediately release a fourth station impulse is received. The r lease of relay 85 in response to a fourth inpuise opens the circuit through the right windings of relays 63 and 64. Relay 63 releases before relay 85 reoperates, but relay 6% remains operated due to its short-circuited left winding. When relay 85 reoperates after the fourth impulse, the reconnection of conductor 161 to in uctance 91 causes the re-energization of the ri ht winding of relay 64 and the energizaticn of the right winding of relay 65. The operation of relay 65 opens the short circuit around the left winding of relay 64, so that 64 may immediately release if a fifth impulse is received by relay 85. The release of relay 85 in response to a fifth station impulse opens the circuit through the right windings of relays c and 65. Relay 64 releases before relay 85 reoperates, but relay 65 remains operated due to its short-circuited left winding. When relay 85 reoperates after the fifth station inipulse, the right winding of relay 65 is again energized to hold this relay operated. It is appar- The operation of relay 64 opens,

ent, therefore, that afterithe entire train of station impulses have been received, relays 6i. and 62 are held operated if one station impulse,

is received; that relays 62 and 63 are held operated if two station impulses are received; that relays 63 and 64 are held operated if three station impulses are received; that relays 64 and 65 are held operated if four station impulses are received; and that relay 65 alone is held operated if five station impulses are received. When relay 85 reoperates after the last station impulse has been received, relay 8'? releases thereby reconnecting the ringing source 90 to conductor 102 of line L to cause the reoperation of relay 60. Relay 60 is again held operated by the energization of its right winding as hereinbefore described. With relays 61 and 62 operated, a

ringing circuit is also established from ground through source over conductor 102 through the middle back contacts of relays 11, 21, 31, 41.and 51 and over conductor 69, through the inner back contact of relay l1 and the winding of relay 11 in parallel with condenser 12, over the lower conductor of extension line 16, key 1 and through the ringer (not shown) at station 1, back over the upper conductor of extension line 10, through the outer right back contact of relay 63, outer right front contact of relay 62, and the inner left front contact of relay 60,

over conductor 101 of line L, terminal andlorush.

of bank 82, right front contact ofrelay 85 and through impedance 91- to grounded battery. With relays 62 and 63 operated, the ringing current path is traced from conductor 69 through the inner back contact of relay 21, winding of relay 21 and condenser 22 in parallel, over extension line 20 and through the ringer at station S2,'through the outer right front contacts of relays 63 and 62, and through the inner front contact of relay 60 to conductor 161. W ith relays 63 and 64 operated, the rin ing current path is traced from conductor 69 through the inner back contact of relay31, winding of relay 31 in parallel with condenser 32, over extension line 30 and through. the ringer at station S8, .through the right back contact of relay 65, outer right front contact of 64, and. through the inner left front contact of relay-6O to conductor 101. With relays 64 and 65 operated, the ringing current path is traced from conductor 69, through the inner left back contactof relay 41, winding of relay 41 in parallel with condenser 42, over extension line .40 and through the ringer at station S4, through the inner right .front contact of relay 65, the outer right front. contact of relay 64, and through the inner left front contact of relay 69 to conductonlill. And with only relay 65 the im" pulse receivingrelays operated, theringing current path" is traced'from conductor 69, through the inner left back contact of relay 51, winding of relay 51 'in parallel with condenser 52, over the extension line 50 and through the ringer at station S5, through. the outer right front contact of relays '65 and the outer right back contact of relay 64, and through the left front contact of relay 60 to conductor 101. Thus, the particular one of stations 81, S3, S4 and S5, which has been selected by relays 61 to 65, inclusive, in response to the impulses repeated over line L by relay 85 of the final selector, is signaled. -Upon removal of thereceiver at the called station, the current is increased sufiiciently to operate relay 88 of the foal selector. Relay 88,1ocks through its right winding under ticular' called station.

the line conductors 101 and 102.

control of release relay 86 and1 disconnects the ringing current source 90 from conductor 102. Relay 88 also connects ground throughinductance 92 and the left back contact of relay 8? 5 and left front contact of relay 88 to conductor 102 in place of the ringing current source 90, thereby establishing a direct current circuit through that one of the cut-off relays ll, 21, 31, 41 and 51 which is associated with the par- 3 is the called station, the cut-off relay 31 is thus operated by the direct current through its winding after the called subscriber has removed the receiver from the receiver hook.

1 5 The operation of relay 31 causes the release 'stored to normal in the well known manner, re-

lays 89 and 77 being thereby released.

The resistance 66, normally short-circuited by the inner right back contact of relay 60, is inserted in series with the right windings of rem'lays 60, 61, 62, 63 and 64 after relay reoperates at the end of the station selection, in order that the cut-oil relay or the selected station will receive a large enough current through its winding to insure its operation when the 3 5 called subscribed answers.

It should be noted that the impulse receiving relays so, 61, 62, 63, 64. and and the cut-off relays 11, 21, 31, 41 and 51 are all operated rom a source of current located at the central M oflice, no additional source of current being pro vided for any of the stations or for the common relay group.

What is claimed is:

1. In a telephone system, a central office; a plu- 'a1ity of subscribers stations, a line connecting all of said stations to said central office, a group of relays operative in response to an incoming call to select any desired one of said stations, and relays one for each of said stations for dis wiconnecting all of the other stations upon receipt of a call at any one of the stations and for dis- 1 connecting all of the other stations upon origination of a call at any one of the stations.

2. In a telephone system, a plurality of sub- 55- .scribers stations, at line common to said stations,

relays one for each of said stations, other relays for said lineand common to said stations, and means at each station for operating the correspondingone of said individual relays whereby the GII'Temainder of said individual relays and said other relays are disconnected from said line.

3. In a telephone system, subscribers stations, a line common to a plurality of said stations, relays one for each of said plurality of stations,

65 other relays for said line and common to said plurality of stations, the operation of any one of said individual relays being effective to disconnect the remainder of said individual relays and said other relays from the line, call initiat- 70 ing means at each of said plurality of stations for operating the corresponding one of said'individual relays, and means for rendering the operation of said call initiating means ineffective so as to prevent interference with incoming calls.

4. In a telephone system, subscribers stations,

Assuming that station a line common to a plurality of said stations, r'elays one for each of said plurality of stations, other relays for said line and common to said plurality of stations, the operation of any one of said individual'relays being effective to disconnect the remainder of said individual relays and said other relays from the line, call initiating means at each of said plurality of stations for operating the corresponding one of said individual relays, a final selector for seizing said line on a call incoming to any one of said stations, and means for rendering the operation of said call initiating means ineffectiva 5. In a telephone system, a line common to a plurality of subscribers stations, selective relays common to said line, means for seizing said line on a call incoming to any one of said stations, and a relay for said line operative in response to ringing current received over said line for operatively connecting said selective relays to said line.

6. In a telephone system, a line common to a plurality of subscribers stations, a final selector for extending incoming calls to said line, selective relays common to said line for extending said line to any particular one of said stations, a ring-up relay operative in response to ringing current received over said line for operatively connecting the first of said selective relays to said line, and a direct current circuit-including. j a source of current in said final selector for holding said ring-up relay and for operating the first of said selective relays.

7. In a telephone system, a line common to a plurality of subscribers stations, a final selector for extending incoming calls to said line, selective relays common to said line for extending said line to any particular one of said stations, a ringup relay operative in response to ringing current received over said line for operatively connecting the first of said selective relays to said line, a direct current circuit including a source of current in said final selector for holding said ringup relay and for operating the first of said selective relays, and a normally short-circuited winding for said first selective relay effective to hold said relay operated during a temporary opening of said direct current circuit.

8. In a telephone system, a line common to a plurality of subscribers stations, a final selector for extending incoming calls to said line, selective relays common to said line for extending said line to any particular one of said stations, a ring-up relay operative in response to ringing current Treceived over said line for operatively j connecting the first of said selective relays to said line, a direct current circuit including a source of current in said final selector for holding said ring-up relay and for operating the first of said selectiverelays, a normally shortcircuited winding for said first selective relay effective to hold said relay operated during a temporary opening of said direct current circuit, and means efiective upon the closing of said direct current circuit after a first temporary opening thereof for operating the second one of said selective relays.

9. In a telephone system, subscribers stations, lines, one of said lines being common to a plurality of said stations, a final selector for select- 3 1:

ing and connecting with said line on calls incoming to any one of said plurality of stations, selective relays common to said line for selecting and connecting said line to any one of said plurality of stations to the exclusion of the other selective relay for preventing the release of said first selective relay during the first opening of said impulse contacts.

10. In a telephone system, subscribers stations, lines, one of said lines being common to a plurality of said stations, a final selector for selecting and connecting with said line on calls incoming to any one of said plurality of stations, selective relays common to said line for selecting and connecting said line to any one of said plurality of stations to the exclusion of the other stations, a ring-up relay responsive to signaling current received over said line from said selector for operatively connecting said selective relays to said line, a direct current circuit for holding said ring-up relay operated and for operating the first of said selective relays, impulse transmitting contacts in said selector for alternately opening and closing said circuit, the first opening being efiective to release said ring-up relay, a second normally short-circuited winding for said first selective relay for preventing the release of said first selective relay during the first opening of said impulse contacts, and a circuit including a bacl; contact of said ring-up relay and said' impulse contacts to operate a second one of said selective relays and hold said first selective relay.

11. In a telephone system, subscribers stations, lines, one of said lines being common to a plurality of said stations, a final selector for selecting and connecting with said line on calls incoming to any one of said plurality of stations, selective relays commonto said line for selecting and connecting said line to any one of said plurality of stations to the exclusion of the other stations, a ring-up relay responsive to si naling current received over said line from said selector for operatively connecting said selective relays to said line, a direct current circuit for holding said ring-up relay operated and for operating the first of said selective relays, impulse transmitting contacts in said selector for alternately opening and closing said circuit, the first opening being effective to release said ring-up relay, a second normally short-circuited Winding for said first selective relay for preventing the release of said first selective relay during the first opening of said impulse contacts, a circuit including a back contact of said ring-up relay and said impulse contacts to operate a second one of said selective relays and hold said first selective relay, and means actuated by the operation of said second selective relay for opening the circuit through the second Winding of said first selective relay.

12. In a telephone system, subscribers stations, lines, one of said lines being common to a plurality of said stations, a final selector for selecting and connecting with said line on calls incoming to any one of said plurality of stations, selective relays common to said line for selecting and connecting said line to any one of said plurality of stations to the exclusion or" the other stations, a ring-up relay responsive to signaling current received over said line from said selector for operativcly connecting said selective relays to said line, a direct current circuit for holding said ring-up relay operated and for operating the first of said selective relays, im-

pulse transmitting contacts in said selector for alternately opening and closing said circuit, a first opening being eiiective to release said ringup relay, a second normally short-circuited Winding for said first selective relay for preventing the release of said first selective relay during the first opening of said impulse contacts, a circuit including a back contact of said ring-up relay and said impulse contacts to operate a second one hold said selective relay, and means actuated by the operation of said second selective relay for opening the circuit through the second Winding said first selective relay to enable the release of said first selective relay in respouse to the second opening of said impulse contacts, and a second normally short-circuited. Winding for said second selective relay for preventing its release during the'second opening of said impulse contacts.

13. In a telephone system, a central ofiice, a plurality of subscribers stations, a line con-' necting all of said stations to said central office, a group of relays operative in response to an incoming call to select any desired one of said stations, relays one for each of said stations for disconnecting all of the other stations upon receipt of a call at any one of the stations and for disconnecting all of the other stations upon origination of a call at any one of the stations,

and a source of current at said central ofiice for operating and holding said group relays and said individual relays.

14. In combination a plurality of selective relays, each relay having ing of each of said selective relays being normally short-circuited, impulse transmitting means, means for operatively connecting said impulse transmitting means to a first one of said selective relays, a circuit including the interrupter contacts of said impulse transmitter and one winding ofsaid first selective relay for operating said relay, means for actuating said impulse transmitter to alternately open and close its" contacts, and a short-circuit acro ss-= interrupter the other winding of said first selective relay to prevent its release during the first opening of said interrupter contacts.

15. In combination a plurality of selective relays, each relay having two windings, one Winding of each of s id selective relays being normally short-circuited, impulse transmitting means, means for operatively connecting said impulse transmitting means to a first one of said selective relays, a circuit including the interrupter contacts of said impulse transmitter and one Winding of said selective relay for operating said relay, means for actuating said impulse transmitter to alternately open and close the interrupter contacts, a short circuit across 4 the other Winding of said first selective relay to prevent its release during the first opening of said interrupter contacts, and means effective in response to the first opening of said interrupts contacts for connecting one Winding of 1115 the second of said selective relays in series with said interrupter contacts.

16. In combination, a plurality of selective relays, each relay having two windings, one winding of each of said said selective relays and 90 tWo windings, one wind- 115 selective relays being normal- 1y short-circuited, impulse transmitting means, means for operatively connecting said impulse transmitting means to a first one of said selective relays, a circuit including the interrupter contacts of said impulse transmitter and one winding of said first selective relay for operating said relay, means for actuating said impulse transmitter to alternately open and close its interrupter contacts, a short circuit across the other winding of said first selective relay to prevent its release during the first opening of said interrupter contacts, means effective in response to the first opening of said interrupter contacts for connecting one winding of the second of said selective relays in series with said interrupter contacts, and a short circuit across the other winding of said second selective relay to prevent its release during a second opening of said interrupter contacts.

17. In combination a plurality of selective relays, each relay having two windings, one Winding of each of said selective relays being normally short circuited, impulse transmitting means, means for operatively connecting said impulse transmitting means to a first one of said selective relays, a circuit including the interrupter contacts of said impulse transmitter and one Winding of said first selective relay for operating said relay, means for actuating said impulse transmitter to alternately open and close its interrupter contacts, a short circuit across the other winding of said first selective relay to prevent its release during the first opening of said interrupter contacts, means effective in response to the first opening of said interrupter contacts for connecting one winding of the second of said selective relays in series with said interrupter contacts, a short circuit across the other winding of said second selective relay to prevent its release during a second opening of said interrupter contacts, and means effective in response to the release of said first selective relay during the second opening of said interrupter contacts for connecting one winding of the third of said selective relays in series with said interrupter contacts.

18. In combination a plurality of selective relays, each relay having two windings, impulse transmitting means, means for operatively connecting said impulse transmitting means to a first one of said selective relays, a circuit including the interrupter. contacts of said impulse transmitter and one winding of said first selective relay for operating said relay, means for actuating said impulse transmitter to alternately open and close its interrupter contacts, a short circuit across the other winding of said first selective relay to prevent its release during the first opening of said interrupter contacts, means effective in response to the first opening of said interrupter contacts for connecting one Winding of the second of said selective relays in series with said interrupter contacts, a short circuit across the other winding of said second selective relay to prevent its release during a second. opening of said, interrupter contacts means effective in response to the release of said first selective relay during the second opening of said interrupter contacts for connecting one winding of the third of said selective relays in series with said interrupter contacts, and a short circuit across the other winding of said third selective relay to prevent its release during a third opening of said interrupter contacts.

WALTER BRANDT. 

